Many hard real-time control systems require the precise control of actuators to control a process or plant or machinery. These actuators must be accurately managed, for example to turn on and off at critical times or angles of rotating machines or at specific voltages or currents.
Control systems are known in which an analog application specific integrated circuit is used, which generally provide a fast, and therefore more accurate control loop, those control systems are expensive and inflexible because they cannot be reconfigured to perform another function in another application.
From U.S. Pat. No. 5,233,573, a microcontroller is known which incorporates a digital timer apparatus and a central processing unit (CPU). The digital timer apparatus receives an external signal. Upon a transition of the external signal, the value of a free-running counter driven by a constant frequency clock signal, is loaded into a capture register and causes a pulse accumulator to be incremented. The pulse accumulator is reset periodically by an interval timer. Thus, both the time of a transition and the number of transitions during a certain period of time can be determined. The time of a transition and the number of transitions are used by the CPU to perform a control function.
However, a disadvantage of this prior art system is that, although a CPU is flexible and can be relatively cheap, the CPU is relatively slow which makes the control slow and imprecise.